In recent years, in a portable electronic device typified by a mobile phone, a digital camera is provided as a standard function. More and more downsizing and weight reduction are constantly required of such a portable electronic device, which inevitably requires downsizing and weight reduction of a camera module. However, in the camera module installed in the portable electronic device, there is a demand for enhancement of functions including an auto-focus function, a camera shake correction function, and the like.
For this improvement of the functions of the camera module, an actuator for driving an optical system and a mechanical structure is essential. Therefore, an actuator that allows improved functions while satisfying the demand for downsizing and weight reduction is required.
For such a demand, an actuator adopting a shape-memory alloy is attracting attentions. In the actuator adopting the shape-memory alloy, the shape-memory alloy is electrically heated to be thereby expanded and contracted, thus causing a displacement. A technique is proposed in which the displacement is indirectly detected based on a detection of a change of a resistance value caused by a deformation of the shape-memory alloy, so that the displacement of the actuator can be freely controlled (for example, Patent Document 1).